The present invention relates to a printed circuit board, and more particularly to a flexible printed circuit board of a high speed computer system which may be folded in order to more efficiently fit within a fluid filled, cylindrical enclosure for cooling.
It is known in the art to mount discrete power semiconductors upon a generally cylindrical, rigid insulated mounting and to cool this combination by a metallic heat sink. It is also known to cool such heat sinks by forced convection, or a combination of convection and thermal conduction. An example of the later is shown in U.S. Pat. Ser. No. 2,984,773 issued May 16, 1961 to Guldemond et al. entitled "ALTERNATING CURRENT RECTIFYING ASSEMBLY". The problem with such devices is that these devices usually only mount components on an outer cylindrical surface because the mounting of components on the interior of the outer cylindrical surface is usually difficult. Thus, it is desirable to provide a printed circuit board for mounting in a generally cylindrical enclosure, which has components mounted on its outer cylindrical surface and also inside the outer cylindrical surface, yet which is easily manufactured.
Another known approach to mounting electrical and/or electronic circuits within a cylindrical enclosure is to put the components onto a flexible printed circuit "board" and then roll the flexible circuit into a spiral. Such an approach is shown in: U.S. Pat. Ser. No. 4,510,551 issued April 9, 1985 to Brainard II, entitled "PORTABLE MEMORY MODULE"; and U.S. Pat. Ser. No. 4,412,272 issued Oct. 25, 1983 to Wedertz et al., entitled "FLEXIBLE PRINTED CIRCUIT CARD ASSEMBLY".
The patent by Brainard II discloses a low power, air cooled, flexible memory module which is spirally wrapped around an inner cylindrical column in which the power source is mounted. Electrical insulation between the spiral layers is provided by a additional insulating sheet, or by the plastic integrated circuit packages acting as their own insulating spacers. In either case, the insulation and cooling characteristics would not be sufficiently defined to use such an approach for a fluid convection/conduction cooled, high speed computer system without a lot of trial and experimentation to get it right.
The patent of Wedertz et al. discloses a multi-layer flexible circuit board in which one of the external layers is a foam material. When the flexible circuit board is rolled into a spiral configuration, the foam separates and insulates the components from each other. To some extent, the foam also provides a type of conduction heat sink for the components. However, the heat sinking characteristics are inadequate for cooling some of the components. This is demonstrated by the alternative embodiment shown with cooling openings therein to provide cooling, and by the suggestion that high heat dissipating components be located near the edges to increase the cooling capacity. Such a design would not lend itself to a high speed, high heat dissipation computer system, which ideally has a freely flowing fluid for conduction/convection cooling of all the components regardless of where they are mounted.
It is an object of this invention to provide a printed circuit board assembly which has flexible panels such that the printed circuit board may be folded and inserted into a container whose dimensions would be too small to receive the printed circuit board assembly in the unfolded state.
It is another object of this invention to provide a printed circuit board assembly which may be folded and inserted into a container that is filled with a cryogenic coolant.
It is a further object of this invention to provide a printed circuit board assembly which may be folded into geometric configurations that permit the free flow of a cryogenic fluid coolant when the assembly is installed into a container.
It is a further object of this invention to provide a printed circuit board assembly which has flexible panels such that the printed circuit board may be folded and inserted into a container whose dimensions would be too small to receive the printed circuit board assembly in the unfolded state, and which has at least one connector between non-adjacent portions of the printed circuit board to reduce a signal path length of the assembly.